Confused about my pet , and a few questions

Hi i recently have been wondering what the numbers are when you level up your pet , my numbers went from (baby) 0 , (adult) 14 , (ancient) 21 , what does the 21 mean? is it like the level of your pet? , and also when hatching a pet why does it cost so much , i went to hatch with a friend and it cost me 50k! i could not believe it cost so much.